Electric double layer capacitor

Abstract

An electric double layer capacitor has an electrode unit ( 10 ), an external lid ( 4 ), an external case, and a gasket ( 8 ) disposed between the external lid ( 4 ) and the external case ( 5 ). The external case ( 5 ) has an open end part that is bent inwardly with the external lid and the external case being disposed so that inner surfaces of the top wall and the bottom wall face each other, to hermetically close an accommodating space, formed by the external case and the external lid. The thickness of at least the circumferential wall of the external lid ( 4 ) is greater than the thickness of the external case ( 5 ). The circumferential wall of the external lid ( 4 ) extends substantially linearly toward the bottom wall of the external case ( 5 ), and the extending edge of the circumferential wall of the external lid ( 4 ) is buried in the gasket ( 8 ).

1 . An electric double layer capacitor comprising: 
 a) an electrode unit having a separator, first and second electrodes opposing each other across the separator therebetween, and an electrolyte solution impregnated in the electrode unit; b) an external lid, formed in a flattened U-shape in cross section, having a top wall and a circumferential wall adjoining the peripheral edge of the top wall; c) an external case, formed in a flattened U-shape in cross section, having a bottom wall and a circumferential wall adjoining the peripheral edge of the bottom wall; and d) a gasket disposed between an outer surface of the external lid and an inner surface of the external case,    the electric double layer capacitor being configured so that the external case has an open end part that is bent inwardly with the external lid and the external case being disposed so that inner surfaces of the top wall and the bottom wall face each other, to hermetically close an accommodating space, formed by the external case and the external lid, for accommodating the electrode unit, wherein:    the thickness of at least the circumferential wall of the external lid is greater than the thickness of the external case; and    the circumferential wall of the external lid extends substantially linearly toward the bottom wall of the external case, and the extending edge of the circumferential wall of the external lid is buried in the gasket.    
   
   
       2 . The electric double layer capacitor according to  claim 1 , wherein the ratio between the thickness of at least the circumferential wall of the external lid and the thickness of the external case is 1.1:1 to 2:1.  
   
   
       3 . The electric double layer capacitor according to  claim 1 , wherein the circumferential wall of the external lid comprises a first circumferential wall having a smaller diameter and adjoining the peripheral edge of the top wall, and a second circumferential wall having a larger diameter and adjoining the first circumferential wall.  
   
   
       4 . The electric double layer capacitor according to  claim 1 , wherein the extending edge has, at a bottom surface thereof, a recessed part into which the gasket fits.  
   
   
       5 . The electric double layer capacitor according to  claim 4 , wherein the recessed part has a depth of from 5  82  m to 50 μm.  
   
   
       6 . The electric double layer capacitor according to  claim 1 , wherein the main component of the gasket is polyether ether ketone.  
   
   
       7 . The electric double layer capacitor according to  claim 1 , wherein the gasket is heat-treated at a temperature higher than a solder melting point.  
   
   
       8 . The electric double layer capacitor according to  claim 7 , wherein the temperature is 260° C.